The present embodiments relate to computer networks and are more particularly directed to a multicast architecture for a virtual private local area network service in a metro Ethernet network.
Ethernet networks have found favor in many applications in the networking industry for various reasons. For example, Ethernet is a widely used and cost effective medium, with numerous interfaces and capable of communications and various speeds up to the Gbps range. Ethernet networks may be used to form a Metro Ethernet Network (“MEN”), which is generally a publicly accessible network that provides a Metro domain, typically under the control of a single administrator, such as an Internet Service Provider (“ISP”). A MEN is typically used to connect between an access network and a core network. The access network typically includes private or end users making connectivity to the network. The core network is used to connect to other Metro Ethernet Networks, and the core network provides primarily a packet switching function.
A MEN typically consists of a number of Provider Edge (“PE”) nodes that are statically identified and configured for communicating with one another prior to the communication of packet traffic. The static plan connects the nodes in a point-to-point manner, that is, each PE node is connected to another PE node in an emulated and bi-directional virtual circuit manner, where each such connection is achieved by a Label Switched Path (“LSP”). An LSP is sometimes informally referred to as a link. Thus, each PE node may communicate to, and receive packets from, an adjacent PE node. Further, along each LSP, between adjacent PE nodes, are often a number of Provider (“P”) nodes. The P nodes maintain no state information and serve primarily a routing function and, thus, are understood not to disturb the point-to-point connection between the PE nodes of the MEN, which are more intelligent devices. A different number of P nodes may be connected in one communication direction between two adjacent PE nodes as compared to the reverse communication direction between those same two adjacent PE nodes. Lastly, note that a PE node in the MEN is also often connected to one or more Customer Edge (“CE”) nodes, where those CE nodes thereby represent the interface between the MEN and an adjacent access network.
With the development of the MEN architecture, there have further evolved additional topologies associated with such a network. One example, that pertains to the preferred embodiments that are later described, is the virtual private local area network service (“VPLS”). A VPLS creates an emulated local area network (“LAN”) segment for a given set of nodes in a MEN. The VPLS delivers an ISO layer 2 broadcast domain that is fully capable of learning and forwarding on Ethernet MAC addresses that is closed to a given set of nodes. Thus, within the VPLS, packets may be broadcast to all nodes on the VPLS. As a broadcast medium, however, the present inventors have observed a potential drawback occurring with respect to multicast communications. Specifically, consider a fully-meshed VPLS MEN. In such a network, each PE node is bi-directionally connected to every other PE node in the VPLS MEN. As such, any PE node may communicate as a source directly along an LSP to any other PE node as a destination, where that destination PE node may respond along another LSP (albeit through a different set of P nodes) in the reverse direction back to the source PE node. A single communication between two PE nodes in one direction and in this manner is referred to in the art as a unicast communication. Complexity arises, however, when a single PE node endeavors to communicate a packet to more than one destination PE node; such a communication by way of contrast is referred to in the art as a multicast communication. In the present state of the art, multicasting in a VPLS MEN is achieved by sending packet traffic on multiple point-to-point interfaces between PE nodes that are already communicating unicast packet traffic. As such, if a particular LSP is particularly burdened by already-existing unicast traffic, then that same LSP is further burdened by the additional multicast traffic that is then sought to communicate along the same LSP. This may be problematic as one or more LSPs carrying delay-sensitive unicast traffic are then disturbed by the addition of the multicast traffic. Also, certain regions of the MEN may be congested while others are not.
Given the preceding, the preferred embodiments are directed to providing an improved MEN VPLS that more efficiently accommodates both unicast and multicast traffic, as described below.